1. Field of the Invention
This invention relates generally to telephone test circuitry and more particularly, it relates to a low cost telephony micro-tester and transport system for testing smaller remote subscriber line carrier (SLC) equipment on a more effective and efficient basis. In particular, the present invention is directed to a telephony micro-tester system which includes a small integrated micro-controller, tip and ring D/A circuitry, tip and ring A/D circuitry, and tip and ring high voltage operational amplifiers for testing accurately subscriber""s telephone lines and/or equipment and which is remotely programmable.
2. Description of the Prior Art
As is generally well-known in the field of telephone communication systems, in the past many years telephone companies have installed large multi-conductor metallic cables either buried underground or suspended above ground between poles or towers. More recently, the telephone companies have replacing the metallic cables with fiber optics cables which are suitable for a digital carrier system. Further, over the last 20 years the telephone companies have installing remote subscriber line carrier (SLC) equipment in pedestals or towers located at spaced apart positions along the underground or aerial cables as well as in residential and commercial facilities.
However, faults sometimes develop in the cables and/or equipment which requires repair or replacement of the same. Thus, the telephone companies have been presently testing the customer""s or subscriber""s telephone lines from the central office (CO) in order to determine the location of the faults so as to know where to dispatch the lineman or repairman. Such tests typically include performing low frequency and DC tests on the customer""s line so as to determine hazardous or foreign potentials, presence of a telephone or ringing, a receiver off-hook (ROH), a short circuit between two or more lines, an open circuit, line length, balance in the line, and sometimes presence of noise.
In order to facilitate the testing for faults in these SLC equipment, the telephone companies have traditionally using an additional copper cable pair to perform the testing. As copper cables were being replaced with the fiber cables, remote testers were used to perform the testing. However, these remote testers suffered the disadvantage of being very slow and expensive in cost. More recently (in the last eight years), the telephone companies have been using a test transparent product consisting of a derived or simulated test pair referred to as a xe2x80x9cmetallic channel unitxe2x80x9d (MCU) which is manufactured and sold by Tollgrade Communications, Inc. of Wilmington, Del. The MCU is used to create a virtual cable pair which can extend the transmission path from the CO of the telephone company to the remote SLC equipment so as to test the customer""s lines. Such a test transparent product is described and illustrated in U.S. Pat. No. 5,457,743 issued on Oct. 10, 1995 and entitled xe2x80x9cMetallic Channel Unit Networkxe2x80x9d, which is assigned to Tollgrade Communications. This ""743 patent is hereby incorporated by reference in its entirety.
There are also known of other tester in the prior art which have developed such as disclosed in International Patent Application No. PCT/US98//07613 filed on Apr. 17, 1998 and entitled xe2x80x9cTelephony Test System With Adjustable Output Impedancexe2x80x9d. This PCT application was assigned Publication No. WO 98/47272 and published on Oct. 22, 1998. The PCT application is assigned to Tollgrade Communications, which is also hereby incorporated by reference.
Specifically, the International Patent Application No. PCT/US98/07613 discloses a telephony test system which includes a controller, a programmable gate array (PGA), and a digital signal processor connected by a common bus. The PGA has its output connected to an input of D/A converter and its input connected to the output of an A/D converter. A driver circuit is connected between the D/A converter and a telephone circuit and between the A/D converter and the telephone circuit. Under the control of the digital signal processor, the driver circuit generates voltages to the telephone circuit and samples the response thereof to such generated voltages. The driver circuit includes control inputs for receiving from the PGA an impedance adjust signal and a resistance adjust signal. An output impedance of the driver circuit connected to the telephone circuit is adjustable as a function of the impedance adjust signal and the resistance adjust signal.
Unfortunately, as the fiber optics cables are installed closer to the subscribers the SLC equipment are now producing smaller SLC systems with line counts of 48, 24, 12, 8 and 6 lines. As a consequence, this has created a testing problem due to the fact that the MCU transparent product and other prior art test systems are too expensive to be used economically for these smaller SLC systems.
Accordingly it would be desirable to provide a low cost telephony micro-tester and transport system for testing these smaller remote SLC systems which is quite accurate and is programmable remotely. The present invention represents a significant improvement over the aforementioned ""743 patent and International Patent Application No. PCT/US98/07613.
Accordingly, it is a general object of the present invention to provide a telephone micro-tester and transport system and method for testing smaller remote SLC customer""s lines and terminal equipment which overcomes the disadvantages of the prior art telephone testing techniques.
It is an object of the present invention to provide a telephone micro-tester and transport system and method for testing smaller remote SLC customer""s lines and terminal equipment on a more economical and efficient basis.
It is another object of the present invention to provide telephone micro-tester and transport system compatible with existing central office testers for testing smaller SLC customers lines and equipment which includes a micro-tester located at a remote terminal for measuring and storing signatures of test performed and a synthesizer located at the telephone company""s central office for re-creating virtual signatures corresponding to the signatures of the test performed by the micro-tester at the remote terminal.
It is still another object of the present invention to provide a telephone micro-tester system for testing smaller SLC customer""s lines and terminal equipment which includes a micro-controller, D/A circuitry, high voltage amplifier driver, A/D attenuator, and A/D circuitry all interconnected for simulating the line through the D/A circuitry and the high voltage amplifier driver and for generating the signatures through the A/D attenuator and the A D circuitry.
In a preferred embodiment of the present invention, there is provided a telephone micro-tester and transport system and method for testing smaller remote SLC customer""s line and terminal equipment which includes a micro-tester located at a remote terminal and a synthesizer located at the telephone company""s central office. The micro-tester is used to measure and store signatures of test performed on the SLC customer""s lines and terminal equipment to determine existing faults. An interconnection path for connecting the micro-tester to the synthesizer is either embedded in the communication channel of a carrier system or provided by modems using one of the carrier channels. A first modem is located at the remote terminal is coupled to the micro-tester for transferring the measured and stored signatures of the test performed to a second modem.
The second modem is located at the telephone company""s central office and receives the measured and stored signatures of the test performed which are being transferred by the first modem. The synthesizer is coupled to the embedded communication channel or the second modem for re-creating virtual signatures corresponding to the signatures of the test performed by the micro-tester and for transporting them to a test system at the telephone company""s central office.